Question about notations

[Hemichordate]

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When you have a notation, say MRD, with two arrows, one going to a number on top and one going to a number below that, does the top number indicate OD and the lower number indicate OS?

 

[MstaKing10]

usually the upper number refers to the right eye (OD) and the lower to the left eye (OS).

 

[guttata]

If you see it written twice (once for each eye), it could represent MRD1 and MRD2.

MRD1 is the distance from the upper eyelid margin to the pupillary center.
MRD2 is the distance from the lower eyelid margin to the pupillary center.